Standard tangent-galvanometer



(No Model.) 4 Sheets-Sheet 1.

E. WESTON.

STANDARD TANGENT GALVANOMBTER; NO. 389.274. Patented Sept. 11, 1888.

WITNEEIEEE, INVENTR` nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn c.

(No Model.) 4. Sheets-Sheet 2.

B. WESTON.

1 STANDARD TANGBNT GALVANOMETER. No. 389,274.

Patented Sept. 11, 1888.

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INVENTU FL .C fiw/ovmm.

(No Model.) 4 Sheets-Sheet 3. B. WESTON.

STANDARD TANGENT GALVANOME-TBR. No. 389,274. Patented Sept. 11, 1888.

WITNESEEE, INVENTUR, ea www (No Model.) i 4 Sheets-Sheet 4. E. WESTON.

STANDARD TANGENT GALVANOMETEB..

No. 389,2'74. Patented Sept. 11, 1888.

UNITE STATES ATENT rrreno EDIVARD IVESTON, OF NEVABK, NEWV JERSEY.

STANDARD TANGENT-GLVANOMETER.

SPECIFICATION forming part of Letters Patent No. 389.274, dated September 11. 1888. Appiicmon inga amy 10, iees. seminomstn. (NU model.)

To all whom it may concern;

Be it known that I, EDWARD TiVEsToN, of Newark, Essex eounty, New Jersey, have invented a new and useful Improvement in Tangent-Galvanometers, of which the following is a specification.

The ordinary form of taugent-galvanometer consists, essentially, of a coil of wire wound in a groove in the'circumference of a circular ring, in the center of which ring the magnetic needle is placed. In order that the magnetic influence of the current on the needle may be the same at whatever angle the ncedle may assume, the length of said needle must be very small compared with the diameter of the coil, and the position of the needle must be such that its central point is at the axis of and also in the same plane with the single coil. It has been found that the error due to the magnetic needle not being infinitely short may be obviated by suspending the needle, not at the center of the coil, but at a point on the axis thereof ata distance from the center equal to one-half the radius of the coil, and it has further been determined that the error due to the center of the needle not being truly at the point above iudicated may be eliminated by arranging a second coil similar to the first at equal distance on the other side of the magnet. In that my hereiuafter-described instrument embodies two coils disposed at equal distances on each side of the magnet which is located on the axial linejoining the centers of said coils, it may be regarded as of the general type of apparatus last above noted. Galvanometers of this description, however, when intended for exact electrical measurements have been found difficult and expensive to manufacture and wanting in aecnracy. Leaviug the question of greatlyinereased and, forgeneral usage, prohibitive cost aside, it by no means follows that the multiplication of delicate parts and adjusting mechanism, as is freqnently done, results in increased certainty in the indications of the instrnment. Error iu one adjnsting device may easily al'fect the Operation of a second, and this of a third, and so on, or mutual interaction, so to speak, of disturbing causes may introduce uucertainty throughout the whole chain, so that the mere Operation of putting aninstrument into eondition for use may easily result in a long,r and tedious series of trials for relative adj ustments, terminating only when a real or more often assumed. condition of equilibrium of the opposing forces is k attained, and this even then may be subject to unknown inaeeuracy dependent upon the personal equation77 of the observer or adjuster.

My invention consists in a standard absolute galvanometer, accurate primaril y and necessarily by reason of its construction. I make it, in other words, so that by reason of its construction its coils when placed on the instrument in their stationary position and on opposite sides of the central standard shall be relatively parallel with their centers equidistant from the longitudinal axis of said standard, and disposed on a line intersecting said longitudinal axis at right angles. \Vithin this standard I support the magnet. It is necessary, then, simply to adjust the movable magnet, so that its center will be at the point of intersection already permanently and exactly established. Therefore thisis aninstrnmentin which the proper position of the magnet with referenee to the coils, and vice versa, is once for all fixed,not by relative adjustments of mag net and coils, but by the absolute relation and positions of the parts of the rigid Structure, whereby said magnet and coils are held and supported. The position of the coils with reference to the magnet is invariable. The point which the magnet center should oeeupy with reference to the coils is fixed and invariable. It remains, then, to move the movable magnet so that its center will be iu that position, or to allow it to take that position naturally, as by the action of gravity upon it. Consequently, in order to render my instrument ready for immediate Operation, the coils being secured in place, I have merely to observe that the maguet is rightly located, and then I can proceed to make absolute electrical measurements with an accuracy not attainable, if at all, other than by the use of the most complieated and delicate adjustmeuts. I also secure certain other features of beuelit, whereby a great range of measurement covering very large and very `small curreuts is obtained, and whereby the manipulatiou of the instrument is simplitied. I also simplify the details of the construction, whereby the necessity for highly-skilled labor iu the manufacture is obviated, the number of parts lessened, and the IOO genteral structure rendered strong and compac In the acconipanying drawings, Figure 1 is a front elevation of my galvanoineter. Fig. 2 is a vertical section of the same. Fig. 3 is a plan View of the base. Fig. 4 is a side elevation and partial sectionof the lower part of the instrument, showing the device for rotating the standard. Figs. 5 and 6 illustrate the mode of producing the standard and supports for the coils on a single pair of centers. Figs. 7 and 8 illustrate,` respectively, the magnet and its relation to the sight-holeT during adjustment. i

Similar letters of reference indicate like parts.

A` is the central holloW supporting column or standard, having at its lower portion a tapering extension, J, which is received in a correspondinglyformed Opening in the center of the tripod-base B. By means of the screw K and washer L the extension J is drawn into the tapering Opening in the base B, and in this way the standard is centrally pivoted to the base. The base B is provided with leveling-screws B', of the nsual construction, located at the ends of the tripod-arms.

The standard A is enlarged at its iniddle portion, and is there bored transversely at m, Fig. 6, to receive the cylindrical block E, of copper or other diamagnetic metal, which constitutes a dampening device and prevents undue oscillation of the needle F, which is'suspended in a central spherical cavity, S, in said block. The block E is divided .transversely into halves and the parts are inserted into the bore of the enlargement of the standard A from opposite Sides, and are connected together by screws G, Figs. 1 and 2. After the block is adjusted in the bore it is Secured in place by the set-screw P, dotted lines, Fig. 1.

The needle or magnet F, as here shown, is of ring shape, as shown in detail in Fig. 7. Extending diametrically across it is a finewire bar, Q, which exactly at its middle point, and hence at the' center of the ring,carries a small circular disk, R. VVhen the magnet is suspended in the Chamber or cavity S in block E, this disk B comes directly in line with a sighthole, T, so that if the disk is accurately centered then a true circle of light will appear around iton looking through the Sight-hole, as indicated on the left of Fig. 8, whereas if it be not properly centered, then the eccentricity will be obvious by their-regular breadth of the light annulus, as shown on the right of Fig. 8.

The particular construction and form of the inagnet F,its arrangementin combination with the block E, the mode of adjusting said magn et, and also the device for attaching it to its suspension-rodmsherein shown,are all disclaimed by nie in this application for the reason that they are fully described and claimed in an-' other application for Letters Patent,Serial N o. 273,518, filed by me simnltaneonsly herewith. Resting in a socket in the npper end of esam standard A is a vertical glass tube, M, at the Upper extremity of which (not shown) is any suitable support, whereto is attached a ISilk or other fiber, which extends down through said tube and into the standard A, and carries a mirror, H. This mirror is seen through an Opening, U, in the side of a Chamber or com' partment, k, in standard A. lt will be observed that I do not cover the Opening U with glass, as is commonly done, in order to protect the mirror from possible air-currents. I find that it is better to leave the face of the mirror exposed, for the reason that the refraction of the glass Shields, often an unknown quantity, is apt to impair the accuracy of the refiected image. Depending from the mirror H is a thin aluminium rod, O, which is connected to and supports the niagnet F. Mirror H and magnet F stand in the same vertical plane, which, when no current traverses the coil, is parallel to the vertical planes passin g through said coils.

Upon thestandard Aaresupportsor brackets I 1 I' I', which preferably are made integral with the said standard. On the opposite faces of these brackets are curved grooves l cut in true arcs of a circle, and receiving the metalflanged ringsVV'. Resting against the rings V V'are the rings D D',which are made ofebonite or other insulating material, and which constitute the spools or bobbins for the coils W W'. The rings V V' and D D' are clamped to the brackets I 1' by means of setscrews a. which pass through said rings and enter said brackets. At the center of the base B is an upwardly-projecting circular boss,b, upon one side of which is formed a toothed segment, c, Figs. 1 and 3. Secured to one side of the bracket 1 1' is a collar, cl, and end bearing, e, for the worm screw f. The thread on screw f engages with the toot-hcd segment c, and hence,`by rotating said screw,said screw moves over the said segnient, and thns rotates the standard A on its vertical axis, the extension J turning in its socket in the base B. Above the enlargement on standard A, and on opposite sides of said standard,are slots N, through which the rod O may be seen. The coil-terminals are shown at g, Fig. 1.

Referring to Figs. 5 and 6, I will now explain my mode of manufacture, wherebylsecure a construction which insures the accuracy of the instrument, as already set forth. In Fig. 5 isshown the blank for thestandard A disposed between the lathe centers h h'. `vVhen the standard is tnrned in the lathe to the desired form, obviously the line extending between said lathe-centers, is the longitudinal axis or center line of the standard, and in this way this line is Very simply fixed. The standard is then applied to the faceiplate of the lathe, as indicated in Fig. 6, and is centered thereon. The face-plate then beingrotated, the groovesl in the brackets I I' 1 I' are formed, and the bottoms of the said grooves, respectively in brackets I I' and in brackets I 1', are made equidistant from the axisi i'; or, in other ICO IIO

Lwords, the grooves Z are in ares of circles struck from centers equidistant from the longitudinal axis 117 fi' and located upon line j j' at right angles to and intersecting said axis. The groovesl, as already stated, conform to the curvcs of the circles of the spools D D' of the coils. Therefore, When said coils are fixed in said grooves, it will follow necessarily, first, that the said coils will stand in parallel plancs and on opposite sides ofthe standard; second, that the centers of said coils Will be equidistant from the longitudinal axis of said standard. It follows, then, that the point of intersection of the linejj' and the axist'i' will be the true position for the magnet. WVhile the standard is centered upon the face-plate the eylindrical bore m, into which theblock E enters, is also turned. If, now, the linej j' be the axis of the bore m and also of the sight-oritice T in the block E,which tits said bore, it follows that When the block is in place therein and the center of the magnet becomes symmetrically adjnsted with reference to said sight-oriliee, as already described, then said magnet center will be accnrately at said point of intersection of axis i i' and linejj', and thns the exact relative positions of coils and the magnet become established. It Will be apparent, therefore, that the precise point for the location of the needle center is thus made fixed definite and inalterable by the actual construction employed. In Operation the base B is leveled by means of the screws B', and the alumininm rod O is observed through the slots N until it appears to have assumcd, as nearly as can be approximated, a true vertical in the standard axis. Then on looking through the Sight-hole T the adj ustment can be more aceurately continued until a ring of light of even breadth appears around the magnet-disk. This done the magnet is aceurately centered and the instrnment is ready for use. The current traversing the coils infiuences a magnet in a way that is'well understood and therefore need not here be described. The mirror H, moving simnltaneously with the magnet, may retlect a reading from a scale disposed in suitable proximity, or retlect a beani of light upon a marked scale, by which means the cxtent of its angular displacement can be determined.

In my present application I do not deseribe any particular arrangement or construction of scale, for the reason that various dispositions therefor are well known and may be adapted to use in connection with the present instrument by any competent electrical workman or other person skilled in the art. The adjusting-serew allows of the standard A being rotated on its vertiealaxias already described, and in this way the coils may be set with reference to the magnetic meridian.

The coil rings D are secured in stationary position to the supports, and may be permanently so fastenedjf desi red. Itis preferable, however, to provide several coils varying in effect upon the magnet, and to this end the turns of the conductors, respectively, on said coils may Vary from the single turn of a large conductor to many turns of a small conduetor. These coils are all to be applied to bobbins or spools of like shapeand diaincnsionsand hcnce all made interehangeable with referenee to the supports I I', &-c. I. provide, also, pairs of coils, the eonductor forming one coil of the pair being` so arranged or constructed as compared With the conductor forniing the other coil that the effect of both jointly upon the needle will depend upon the ratio cxistingbetween the said conductors, and this ratio l mark in suitable characters upon the pairs of coils themselvcs.

lnasinueh as the position of the coils with reference to the magnet center is made fixed and invariable, it follows that the constant of the instrument may once for all be determined for each coil. Referring to the well-k now n expression for the constant for a single coil, in which a is the distance of the coil from the magnet-center, it is obvious that in the present instrument this distance is once for all fixed; hcnce it is necessary simply to divide this eonstant by the number of turns of the coil to determine the Constant of the instruxnent for any particular coil of more than one turn; The quotient innltiplied by the tangcnt of the angle of (leviation of the inagnet and by the strength of the earthfs magnetism at the place where used gives the measurement of the current in absolnte electro-magnetic units.

I claina- 1. In a galvanometer, a hollow standard, a vibrating` magnet thcrein, fixed supports integrally formed of said standard and upon opposite sides thereof, coils received by said supports and held in parallel planes, and means for securing said coils to rsaid supports, substantially as described.

2. In a galvanometer, a hollow standard, a vibrating magnet thcrein, two parallel stationary coils fixed upon opposite sides of said standard, and means for adjusting the center of said magnet into eoincidenee with a line joining the centers of said coils, substantially as described.

3. In a galvanometer,a vertical hollow standard, al magnet suspended therein, and two stationary parallel coils fixed upon opposite sides ot said standard, the centerof said magnet eoineiding with the point of intcrseetion of the Vertical axis ot' said standard, and in line with the centers ofsaid coils,substantially as described.

4. l'n agalvanoinetcna central hollow standard, a Vibrating magnet thcrein, King-supports on opposite sides thereof, coils, and means for securing said coils to said ring-supports, the arcs of said ring-supports being struck from centers located on a line interseeting and at right angles to the longitudinal axis of the standard, substantially as described.

5. Ina galvanometer, a vertical holloW stand- IOO ard, abiock ofdiamagnetic metal containing a centrai Chamber and supportedinsaidstandard, a magnet suspended from the upper part of said standard and Within said central chamher, and two stationary coi1s,respectivei y supported upon and on opposite sides of said standard in parallci pianes, substantiaiiy as described.

6. In a gaivanometer containing a vertical holiow standard and a magnet suspended theren, an open chamber in said standard and a mirror conneeted to and partaking of the motion of said magnet arranged within said ehamhor, substantially as described.

7. In combination with agalvanomeler containing vibrating magnet, coils, supports, and a means forsecuring said coils to said supports, two or more coils of differentinductive capacities interchangeabiy adapted lo said supports, substantially as described.

8. In combination With a gaivanometer containing a vibratiug needle, coii, supports, and a means for attaching coils to said supports, two coils of different inductive capacities interchangeabiy adapted to said supports and marked with characters indieating the ratio of their respective capacities, substantially as described.

9. The combination, in a galvanometer containing a vibrating magnet and coils disposed on opposite sides thereof, of the hollow standard A, receiving the magnet, and provided with supports I 1', for the coils, snbstantially as described.

' 10. The combination, in a galvanometer containing a vibrating magnet and coils disposed on opposite sides thereof, of the hollow standard A, provided on opposite sides with fixcd supports I', having curved grooves for the rceeption of the coils, the arcs of the curves of said grooves being struck from centersequidistantiy' located from the longitndinai axis i i' of said standard and upon a 1ine,jj', intersecting and at right angles to said longitudinai axis, substantiaily as described.

11. The combination of the hoiiow'standard A, vibrating magnet therein, supports I I' 1 I', rings O, coils D, and ciamping screws a, substantiali y as described.

412. The combination ofthe standard A, having the conieal extension J, base B, washer L, and screw-boit K, snbstantially as described.

13. Thecombination ofthe standard A, supports 1 I'f'thereon, worm-serew f, and supports d e therefor, with the base B, having boss b,and toothed segment c on said boss,substant-ially as described.

EDWTARD \VESTON.

vitnesses:

EDW. E. QUIMBY, PARK BENJAMIN. 

